U.S. patent application number 11/750821 was filed with the patent office on 2008-11-20 for error driven rf power amplifier control with increased efficiency.
This patent application is currently assigned to QUANTANCE, INC.. Invention is credited to Serge Francois Drogi, Martin Tomasz, Vikas Vinayak.
Application Number | 20080284510 11/750821 |
Document ID | / |
Family ID | 40026914 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080284510 |
Kind Code |
A1 |
Drogi; Serge Francois ; et
al. |
November 20, 2008 |
ERROR DRIVEN RF POWER AMPLIFIER CONTROL WITH INCREASED
EFFICIENCY
Abstract
A power amplifier controller for adjusting a supply voltage to a
power amplifier. The power amplifier controller adjusts the supply
voltage so that distortion in an RF output signal corresponds to a
predetermined limit. An amplitude error signal is generated by the
power amplifier controller which represents a difference between an
RF output signal and an attenuated RF output signal. The AC
components of the amplitude error signal are processed to generate
a deviation signal that represents the distortion in the RF output
signal. The supply voltage to the power amplifier is increased when
the deviation signal exceeds a distortion level control signal, and
decreased when the deviation signal drops below the distortion
level control signal.
Inventors: |
Drogi; Serge Francois;
(Flagstaff, AZ) ; Vinayak; Vikas; (Menlo Park,
CA) ; Tomasz; Martin; (San Francisco, CA) |
Correspondence
Address: |
FENWICK & WEST LLP
SILICON VALLEY CENTER, 801 CALIFORNIA STREET
MOUNTAIN VIEW
CA
94041
US
|
Assignee: |
QUANTANCE, INC.
San Mateo
CA
|
Family ID: |
40026914 |
Appl. No.: |
11/750821 |
Filed: |
May 18, 2007 |
Current U.S.
Class: |
330/136 |
Current CPC
Class: |
H03F 1/34 20130101; H03G
3/004 20130101; H03F 1/0222 20130101 |
Class at
Publication: |
330/136 |
International
Class: |
H03G 3/20 20060101
H03G003/20 |
Claims
1. A radio frequency (RF) power amplifier system, comprising: a
power amplifier coupled to receive and amplify an RF input signal
to generate an RF output signal; and a power amplifier controller
coupled to the power amplifier for controlling a supply voltage to
the power amplifier, the supply voltage adjusted based on a supply
voltage control signal representing a difference between a
deviation signal and a predetermined distortion level control
signal, the deviation signal based on a measured level of activity
of an amplitude error signal, the amplitude error signal based on
an amplitude difference between an amplitude of the RF input signal
and an attenuated amplitude of the RF output signal, and the
predetermined distortion level control signal corresponding to an
allowable distortion level in the RF output signal.
2. The RF power amplifier system of claim 1, wherein the supply
voltage is adjusted in intervals, and maintained constant between
the intervals.
3. The RF power amplifier system of claim 2, wherein power of the
RF input signal is adjusted to compensate for a change of gain of
the power amplifier responsive to the supply voltage being
adjusted.
4. The RF power amplifier system of claim 2, wherein the power
amplifier controller comprises a track and hold module, the track
and hold module in a track mode providing a track and hold signal
that tracks the supply voltage control signal, and the track and
hold module in a hold mode maintaining the track and hold at a
constant level, wherein the track and hold module transitions
between the track mode and the hold mode responsive to an enable
signal.
5. The RF power amplifier system of claim 2, further comprising a
power supply coupled between the power amplifier and the power
amplifier controller to provide the supply voltage to the power
amplifier based on the supply voltage control signal, wherein: the
power supply operates in a fast mode in which the power supply
output voltage is adjustable at a first rate using a first supply
current, the power supply operating in the fast mode during the
intervals for adjusting the supply voltage; and the power supply
operates in a slow mode in which the power supply output voltage is
adjustable at a second rate using a second supply current, the
second rate slower than the first rate, the second supply current
lower than the first supply current, the power supply operating in
the slow mode during times the supply voltage is maintained
constant.
6. The RF power amplifier system of claim 1, wherein the power
amplifier controller comprises: a comparator for generating the
amplitude error signal based on the difference between a logarithm
of the amplitude of the RF input signal and a logarithm of the
amplitude of the attenuated RF output signal; a DC blocking module
coupled to the comparator, the DC blocking module passing AC
components of the amplitude error signal and blocking a DC
component of the amplitude error signal; a deviation detector
generating the deviation signal based on the AC components of the
amplitude error signal; and an error amplifier coupled to the
deviation detector for comparing the deviation signal with the
predetermined distortion level control signal to generate the
supply voltage control signal.
7. The RF power amplifier system of claim 6, wherein the deviation
detector generates the deviation signal based on an average of the
magnitude of the AC components of the amplitude error signal.
8. The RF power amplifier system of claim 6, wherein the deviation
detector generates the deviation signal based on a peak excursion
of the AC components of the amplitude error signal.
9. The RF power amplifier system of claim 6, further comprising a
power supply coupled to receive the supply voltage control signal,
the power supply comprising: a first power supply with a first
adjustment speed receiving a first portion of the supply voltage
control signal and generating a first adjusted supply output based
on the first portion of the supply voltage control signal; and a
second power supply with a second adjustment speed higher than the
first adjustment speed, the second power supply receiving a second
portion of the supply voltage control signal and generating a
second adjusted supply output based on the second portion of the
supply voltage control signal, a combination of the first adjusted
supply output and the second adjusted supply output forming the
supply voltage to the power amplifier.
10. The RF power amplifier system of claim 1 wherein the power
amplifier controller comprises a digital signal processor (DSP)
generating the supply voltage control signal based on the amplitude
error signal
11. The RF power amplifier system of claim 1, further comprising: a
variable gain amplifier (VGA) coupled to the power amplifier for
adjusting the amplitude of the RF input signal based upon a gain
control signal, the gain control signal adjusting the gain of the
VGA in order to maintain constant amplitude difference between the
RF output signal and the RF input signal.
12. The RF power amplifier system of claim 11, wherein the supply
voltage control signal is adjusted in intervals, and maintained
constant between the intervals.
13. The RF power amplifier system of claim 12, further comprising a
first track and hold module, the first track and hold module in a
track mode providing a first track and hold signal that tracks the
supply voltage control signal, and the first track and hold module
in a hold mode maintaining the first track and hold signal at a
constant level, wherein the track and hold module transitions
between the track mode and the hold mode responsive to an enable
signal.
14. The RF power amplifier system of claim 12, further comprising a
power supply coupled between the power amplifier and the power
amplifier controller to provide the supply voltage to the power
amplifier based on the supply voltage control signal, wherein: the
power supply operates in a fast mode in which the power supply
output voltage is adjustable at a first rate using a first supply
current, the power supply operating in the fast mode during the
intervals for adjusting the supply voltage; and the power supply
operates in a slow mode in which the power supply output voltage is
adjustable at a second rate using a second supply current, the
second rate slower than the first rate, the second supply current
lower than the first supply current, the power supply operating in
the slow mode during times the supply voltage is maintained
constant.
15. The RF power amplifier system of claim 13, further comprising a
second track and hold module, the second track and hold module in a
track mode providing a second track and hold signal that tracks the
gain control signal allowing a gain of the gain control signal to
be adjusted, and the second track and hold module in a hold mode
maintaining the second track and hold signal at a constant level,
wherein the second track and hold module transitions between the
track mode and the hold mode responsive to the enable signal.
16. The RF power amplifier system of claim 11, wherein the power
amplifier controller comprises; a comparator for generating the
amplitude error signal based on difference between a logarithm of
the amplitude of the RF input signal and a logarithm of the
amplitude of the attenuated RF output signal; a DC blocking module
coupled to the comparator, the DC blocking module passing AC
components of the amplitude error signal and blocking a DC
component of the amplitude error signal; a deviation detector
generating the deviation signal based on the AC components of the
amplitude error signal; an error amplifier coupled to the deviation
detector for comparing the deviation signal with the predetermined
distortion level control signal to generate the supply voltage
control signal; and a VGA control coupled to the comparator and the
VGA, the VGA control generating a gain control signal based on the
amplitude error signal.
17. A radio frequency (RF) power amplifier system, comprising: a
power amplifier coupled to receive and amplify an RF input signal
to generate an RF output signal; a variable gain amplifier (VGA)
coupled to the power amplifier for adjusting the amplitude of the
RF input signal based upon a gain control signal, the gain control
signal adjusting the gain of the VGA in order to maintain constant
difference between the RF output signal and the RF input signal; a
power amplifier controller coupled to the power amplifier for
controlling a supply voltage to the power amplifier; and the supply
voltage adjusted based on a supply voltage control signal
representing a difference between a deviation signal and a
predetermined distortion level control signal, the deviation signal
based on a time-varying change of gain of the VGA, the
predetermined distortion level control signal corresponding to an
allowable distortion level in the RF output signal.
18. The RF power amplifier system of claim 17, wherein the power
amplifier controller further comprises: a comparator for generating
the amplitude error signal based on the difference between a
logarithm of the amplitude of the RF input signal and a logarithm
of the amplitude of the attenuated RF output signal; a DC blocking
module coupled to the VGA control, the DC blocking module passing
the AC components of the gain control signal and blocking a DC
component of the gain control signal; a deviation detector
generating the deviation signal based on the AC components of the
gain control signal; an error amplifier coupled to the deviation
detector for comparing the deviation signal with the predetermined
distortion level control signal to generate the supply voltage
control signal; and a VGA control coupled to the comparator and the
VGA for generating the gain control signal based on the amplitude
error signal, a linear change in gain control signal causing a
logarithmic change in the gain of the VGA.
19. The RF power amplifier system of claim 18, wherein the
deviation detector generates the deviation signal based on an
average of magnitude of the AC components of the gain control
signal.
20. The RF power amplifier system of claim 18, wherein the
deviation detector generates the deviation signal based on a peak
excursion of the AC components of the gain control signal.
21. The RF power amplifier system of claim 18, the power amplifier
controller further comprising a power supply coupled to receive the
supply voltage control signal, the power supply comprising: a first
power supply with a first adjustment speed receiving a first
portion of the supply voltage control signal and generating a first
adjusted supply output based on the first portion of the supply
voltage control signal; and a second power supply with a second
adjustment speed higher than the first adjustment speed, the second
power supply receiving a second portion of the supply voltage
control signal and generating a second adjusted supply output based
on the second portion of the supply voltage control signal, a
combination of the first adjusted supply output and the second
adjusted supply output forming the supply voltage to the power
amplifier.
22. The RF power amplifier system of claim 17, wherein the supply
voltage control signal is adjusted in intervals, and maintained
constant between the intervals.
23. The RF power amplifier system of claim 22, further comprising a
track and hold module, the track and hold module in a track mode
providing a track and hold signal that tracks the supply voltage
control signal, and the track and hold module in a hold mode
maintaining the track and hold signal at a constant level, wherein
the track and hold module transitions between the track mode and
the hold mode responsive to an enable signal.
24. The RF power amplifier system of claim 23, further comprising a
power supply coupled between the power amplifier and the power
amplifier controller to provide the supply voltage to the power
amplifier based on the supply voltage control signal, wherein: the
power supply operates in a fast mode in which the power supply
output voltage is adjustable at a first rate using a first supply
current, the power supply operating in the fast mode during the
intervals for adjusting the supply voltage; and the power supply
operates in a slow mode in which the power supply output voltage is
adjustable at a second rate using a second supply current, the
second rate slower than the first rate, the second supply current
lower than the first supply current, the power supply operating in
the slow mode during times the supply voltage is maintained
constant.
25. The RF power amplifier system of claim 23, further comprising a
second track and hold module, the second track and hold module in a
track mode providing a second track and hold signal that tracks the
gain control signal allowing a gain of the gain control signal to
be adjusted, and the second track and hold module in a hold mode
maintaining the second track and hold signal at a constant level,
wherein the second track and hold module transitions between the
track mode and the hold mode responsive to the enable signal.
26. The RF power amplifier system of claim 17 wherein the power
amplifier controller comprises a digital signal processor (DSP) for
generating the supply voltage control signal based on the gain
control signal.
27. A method of amplifying an RF input signal using a power
amplifier, comprising: amplifying the RF input signal by the power
amplifier to generate an RF output signal; generating an amplitude
error signal based on an amplitude difference between an amplitude
of the RF input signal and an attenuated amplitude of the RF output
signal; generating a supply voltage control signal based on a
difference between a deviation signal and a predetermined
distortion level control signal, the deviation signal based on a
measured level of activity of the amplitude error signal; and
adjusting a supply voltage to the power amplifier based on the
supply voltage control signal.
28. The method of claim 27, wherein the supply voltage is adjusted
in intervals, and maintained constant between the intervals.
29. The method of claim 27 wherein the step of generating the
supply voltage is performed by a digital signal processor
(DSP).
30. The method of claim 27 further comprising: adjusting the
amplitude of the RF input signal based upon a gain control signal;
and adjusting the gain control signal to maintain constant the
difference between the RF output signal and the RF input
signal.
31. A method of amplifying an RF input signal using a power
amplifier, comprising: amplifying the RF input signal by the power
amplifier to generate an RF output signal; adjusting amplitude of
the RF input signal by a variable gain amplifier (VGA) based on a
gain control signal to maintain constant a difference between the
RF output signal and the RF input signal; generating an amplitude
error signal based on an amplitude difference between an amplitude
of the RF input signal and an attenuated amplitude of the RF output
signal; generating a supply voltage control signal based on a
difference between a deviation signal and a predetermined
distortion level control signal, the deviation signal based on a
time-varying change of gain of the VGA; adjusting a supply voltage
to the power amplifier based on the supply voltage control
signal.
32. The method of claim 31, wherein the supply voltage control
signal is adjusted in intervals, and maintained constant between
the intervals.
33. The method of claim 31 wherein the step of generating the
supply voltage control signal is performed by a digital signal
processor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a circuit for controlling
RF PAs (Radio Frequency Power Amplifiers), and more specifically,
to an RF PA controller circuit that adjusts the supply voltage of
RF PAs.
[0003] 2. Description of the Related Art
[0004] RF (Radio Frequency) transmitters and RF power amplifiers
are widely used in portable electronic devices such as cellular
phones, laptop computers, and other electronic devices. RF
transmitters and RF power amplifiers are used in these devices to
amplify and transmit the RF signals remotely. RF PAs are one of the
most significant sources of power consumption in these electronic
devices, and their efficiency has a significant impact on the
battery life of these portable electronic devices. For example,
cellular telephone makers make great efforts to increase the
efficiency of the RF PA systems, because the efficiency of the RF
PAs is one of the most critical factors determining the battery
life of the cellular telephone and its talk time.
[0005] FIG. 1 illustrates a conventional RF transmitter circuit,
including a transmitter integrated circuit (TXIC) 102 and an
external power amplifier (PA) 104. In some cases, there may be a
filter between the TXIC 102 and the PA 104. For example, the RF
transmitter circuit may be included in a cellular telephone device
using one or more cellular telephone standards (modulation
techniques) such as UMTS (Universal Mobile Telephony System) or
CDMA (Code Division Multiple Access), although the RF transmitter
circuit may be included in any other type of RF electronic devices.
For purposes of illustration only, the RF transmitter circuit will
be described herein as a part of a cellular telephone device. The
TXIC 102 generates the RF signal 106 to be amplified by the PA 104
and transmitted 110 remotely by an antenna (not shown). For
example, the RF signal 106 may be an RF signal modulated by the
TXIC 102 according to the UMTS or CDMA standard.
[0006] The RF power amplifier 104 in general includes an output
transistor (not shown) as its last amplification stage. When an RF
modulated signal 106 is amplified by the PA 104, the output
transistor tends to distort the RF modulated signal 106, resulting
in a wider spectral occupancy at the output signal 110 than at the
input signal 106. Since the RF spectrum is shared amongst users of
the cellular telephone network, a wide spectral occupancy is
undesirable. Therefore, cellular telephone standards typically
regulate the amount of acceptable distortion, thereby requiring
that the output transistor fulfill high linearity requirements. In
this regard, when the RF input signal 106 is amplitude-modulated,
the output transistor of the PA 104 needs to be biased in such a
way that it remains linear at the peak power transmitted. This
typically results in power being wasted during the off-peak of the
amplitude of the RF input signal 106, as the biasing remains fixed
for the acceptable distortion at the peak power level.
[0007] Certain RF modulation techniques have evolved to require
even more spectral efficiency, and thereby forcing the PA 104 to
sacrifice more efficiency. For instance, while the efficiency at
peak power of an output transistor of the PA 104 can be above 60%,
when a modulation format such as WCDMA is used, with certain types
of coding, the efficiency of the PA 104 falls to below 30%. This
change in performance is due to the fact that the RF transistor(s)
in the PA 104 is maintained at an almost fixed bias during the
off-peak of the amplitude of the RF input signal 106.
[0008] Certain conventional techniques exist to provide efficiency
gains in the PA 104. One conventional technique is EER (Envelope
Elimination and Restoration). The EER technique applies the
amplitude signal (not shown in FIG. 1) and the phase signal (not
shown in FIG. 1) of the RF input signal 106 separately to 2 ports
of the power amplifier 104, i.e., its supply voltage port (Vcc) 108
and its RF input port 107, respectively. However, the EER technique
often fails to provide significant efficiency gains, because the
supply voltage 108 cannot be varied in an energy-efficient way to
accommodate the large variations in the amplitude signal of the RF
input signal 106; and thus, it fails to provide a substantial
energy efficiency gain while maintaining the required linear
amplification of the RF signal in the PA 104. This is mainly due to
the difficulty in realizing a fast, accurate, wide range, and
energy efficient voltage converter to drive the supply voltage of
the PA 104.
[0009] The conventional EER technique can function better only if a
variable power supply with a very large variation range is used to
adjust the supply voltage based on the amplitude signal of the RF
input signal 106, while not reducing the efficiency of the RF
transmitter by the power consumed by the power supply itself.
However, the variable power supply, which is typically comprised of
a linear regulator (not shown in FIG. 1) that varies its output
voltage on a fixed current load such as the PA 104 in linear mode,
by principle reduces the supply voltage at constant current and by
itself consumes the power resulting from its current multiplied by
the voltage drop across the linear regulator when there is a large
drop in the amplitude signal of the RF input signal 106. This
results in no change in the overall battery power being consumed by
the RF transmitter because any efficiency gained in the PA 104 is
mostly lost in the linear regulator itself.
[0010] Variations of the EER technique, such as Envelope Following
and other various types of polar modulation methods, likewise fails
to result in any significant gain in efficiency in the RF
transmitter, because the supply voltage is likewise adjusted based
on the amplitude signal of the RF input signal 106 which inherently
has large variations; and thus, has the same deficiencies as
described above with respect to conventional EER techniques.
[0011] Some other conventional techniques improve the efficiency in
the PA 104 by lowering the supply voltage 108 to the PA 104. In
many of these techniques, both amplitude and phase components of
the RF input signal 106 are fed to the PA 104 in a conventional
manner. By using a lower supply voltage 108, the PA 104 operates
with increased power efficiency because it operates closer to the
saturation point. However, the supply voltage 108 cannot be reduced
too low, because this would cause the PA 104 to operate with
insufficient voltage headroom, resulting in unacceptable
distortion. As described previously, the distortion may cause
energy from the transmitted signal to spill over to adjacent
channels, increasing spectral occupancy and causing interference to
radios operating in those neighboring channels. Thus, an optimal
supply voltage can be chosen for the PA which balances acceptable
distortion with good efficiency.
[0012] One conventional method uses a step-down switched mode power
supply (SMPS) (i.e., buck regulator) to lower the supply voltage
108 to the PA 104. However, choosing a fixed power supply voltage
is not sufficient in many applications. For example, in most
cellular systems, the PA output power changes frequently because
the basestation commands the cellular handset to adjust its
transmitted power to improve network performance, or because the
handset changes its transmitted information rate. When the PA
output power changes, the optimum supply voltage for the PA (as
described above) changes.
[0013] Therefore, in some systems, the expected power of the RF
output signal 110 is first determined, and then the power supply
voltage 108 is adjusted in accordance with the expected power. By
adaptively adjusting the supply voltage 108, the efficiency of the
PA 104 is increased across various PA output power levels.
Conventional methods estimate the expected power of the RF output
signal 110 in an "open loop" manner, in which the power of the RF
output signal 110 is estimated from the power of the delivered RF
input signal 106. This method does not yield an accurate estimate
of the power of the RF output signal 110 because the estimated
power may vary according to various operating conditions, such as
temperature and frequency. Therefore, even if the estimated power
at some point approximates the actual power, changes in operating
conditions result in deviation of the estimated power from the
actual power.
[0014] Moreover, an estimate of the power of the RF output signal
110 may not be sufficient for properly adjusting the supply voltage
108. For example, the peak-to-average ratio (PAR) needs to be known
in order to estimate the optimum supply voltage for the PA. The PAR
refers to the difference of the mean amplitude and the peak
amplitude in the modulated RF output signal 110. With a higher PAR,
a higher supply voltage is needed to accommodate the peak voltage
swings of the RF output signal 110. Many modern cellular systems
change the PAR of the modulation in real time, requiring the supply
voltage to be adjusted accordingly. Therefore, the conventional
method of adjusting the supply voltage 108 of PA 104 based on an
estimate of the PA output power is unsuitable in these cellular
systems.
[0015] Further, the load presented to the PA 104 poses another
problem. The PA 104 normally drives circuitry usually consisting of
a filter and an antenna. Such circuitry often has an impedance
around the range of 50 ohms. The impedance of the circuitry can
sometime change radically. For example, if the antenna is touched
or the cellular device is laid down on a metal surface, the
impedance of the circuitry changes. The changes in the impedance of
the circuitry coupled to the PA 104 may require changes in the
supply voltage to the PA 104 to prevent distortion of the RF output
signal 110 fed to this circuitry. The conventional methods
described above, however, do not adjust the supply voltage in
response to changes in the impedance of the circuitry.
[0016] Although the problems of inaccurate estimation of power at
the RF output signal 110, changing PAR, and impedance changes at
the output of PA 104 can be avoided by constantly providing a
higher than optimum supply voltage to the PA 104, the higher supply
voltage leads to a less efficient PA 104.
[0017] Thus, there is a need for a PA system that is efficient over
a wide variety of modulation techniques and results in a
significant net increase in power efficiency of the PA system.
Additionally, there is a need for a PA controller that can adjust
the power supply for the PA under conditions of varying
temperature, frequency, output power, PAR, and impedance to
maximize the PA efficiency while keeping distortion to an
acceptable level.
SUMMARY OF THE INVENTION
[0018] In a first embodiment of the present invention, a power
amplifier controller adjusts supply voltage to a power amplifier so
that the distortion of the RF output signal from the power
amplifier corresponds to a predetermined level. In this embodiment,
an amplitude difference between an amplitude of a RF input signal
and an attenuated amplitude of the RF output signal is determined
to generate an amplitude error signal. Then, a deviation signal is
determined from a measured level of activity of the amplitude error
signal to indicate the level of distortion in the output signal.
The deviation signal is then compared with a predetermined
distortion level control signal, to generate a supply voltage
control signal, which in turn adjusts the supply voltage to the
power amplifier. The distortion level control signal is set to
represent an acceptable distortion level at the RF output signal.
Thus, a control loop is created to servo the supply voltage to the
power amplifier in a manner which targets an acceptable distortion
level in the RF output signal.
[0019] In a second embodiment, the power amplifier controller
includes a variable gain amplifier (VGA) coupled to the power
amplifier for adjusting the amplitude of the RF input signal ahead
of the power amplifier. The VGA is adjusted by a gain control
signal based on the amplitude error signal; and thus, operates in a
closed loop manner in which the VGA adjusts the input to the power
amplifier to provide some correction for distortion at the RF
output signal. This distortion correction allows the PA to operate
closer to its saturation point; and thus, allows further decrease
in a supply voltage to the PA compared to the first embodiment,
thereby further increasing the PA's efficiency.
[0020] In a third embodiment, the VGA is included as in the second
embodiment, but the deviation signal is determined from the
time-varying gain of the VGA, which is indicative of the correction
applied by the VGA, and therefore indicative of the distortion in
the RF output signal. An advantage of this embodiment is that the
time-varying gain of the VGA can be measured at the relatively
large signal which controls the VGA's gain, providing a preferred
method of indicating the distortion in the RF output signal.
[0021] An advantage of the power amplifier controller according to
the embodiments of the present invention is that it greatly
increases the efficiency of the power amplifier by keeping the
supply voltage of the power amplifier as low as possible while
maintaining the distortion of the output signal near a
predetermined level. Moreover, because the supply voltage of the
power amplifier is adjusted according to the level of distortion in
the output signal, the supply voltage can be accurately
established, thus maximizing the overall efficiency of the power
amplifier.
[0022] The features and advantages described in the specification
are not all inclusive and, in particular, many additional features
and advantages will be apparent to one of ordinary skill in the art
in view of the drawings, specification, and claims. Moreover, it
should be noted that the language used in the specification has
been principally selected for readability and instructional
purposes, and may not have been selected to delineate or
circumscribe the inventive subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings.
[0024] FIG. 1 illustrates a conventional RF transmitter
circuit.
[0025] FIG. 2 illustrates a schematic diagram of an RF transmitter
circuit including a PA controller in accordance with the present
invention.
[0026] FIG. 3A illustrates an RF power amplifier system, in
accordance with a first embodiment of the present invention.
[0027] FIG. 3B illustrates an RF power amplifier system, in
accordance with a second embodiment of the present invention.
[0028] FIG. 3C illustrates an RF power amplifier system, in
accordance with a third embodiment of the present invention.
[0029] FIGS. 4A and 4B illustrate a method of controlling an RF
power amplifier system, in accordance with the first and second
embodiments of the present invention.
[0030] FIGS. 5A and 5B illustrate a method of controlling an RF
power amplifier system, in accordance with the third embodiment of
the present invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0031] The Figures (FIG.) and the following description relate to
preferred embodiments of the present invention by way of
illustration only. It should be noted that from the following
discussion, alternative embodiments of the structures and methods
disclosed herein will be readily recognized as viable alternatives
that may be employed without departing from the principles of the
claimed invention.
[0032] Reference will now be made to several embodiments of the
present invention(s), examples of which are illustrated in the
accompanying figures. Wherever practicable similar or like
reference numbers may be used in the figures and may indicate
similar or like functionality. The figures depict embodiments of
the present invention for purposes of illustration only. One
skilled in the art will readily recognize from the following
description that alternative embodiments of the structures and
methods illustrated herein may be employed without departing from
the principles of the invention described herein.
[0033] FIG. 2 illustrates a schematic diagram of an RF transmitter
circuit including a PA controller 202 in accordance with the
present invention. The overall function of PA controller 202 is to
adjust the supply voltage 208 to a PA 104 to a level as low as
possible while maintaining the distortion of the RF output signal
110 near an acceptable limit (e.g. a limit defined by standards
covering the RF device, such as 3GPP specifications). By keeping
the supply voltage 208 of the PA 104 as low as possible, the
efficiency of the PA 104 is increased greatly.
[0034] The RF transmitter circuit of FIG. 2 includes, among other
components, a transmitter integrated circuit (TXIC) 102, a PA
controller 202, a power supply 299, an attenuator 254, and the PA
104. The power supply 299 is coupled to a supply voltage V.sub.BATT
210 to provide a supply voltage 208 to the PA 104. The PA
controller 202 includes, among other components, an amplitude
comparator 228, a deviation measuring module 216, and an error
amplifier 288. The amplitude comparator 228 receives the RF input
signal 204 and an attenuated 238 RF output signal 110 as attenuated
by the attenuator 254. The attenuator 254 may be adjusted such that
the output 110 of the PA 104 is attenuated to have an amplitude
level corresponding to the amplitude level of the RF input signal
204. The RF input signal 204 and the attenuated RF output signal
238 are then fed to the amplitude comparator 228 to generate an
amplitude error signal 218 indicative of the amplitude difference
between the RF input signal 204 and the attenuated RF output signal
238. The deviation measuring module 216 measures the activity in
the amplitude error signal 238 and generates a deviation signal 250
indicative of the distortion in the RF output signal 110 relative
to the RF input signal 204. The deviation signal 250 is then
compared with a distortion level control signal 212 defining the
level of distortion allowed in the RF output signal 110.
[0035] During the operation of the RF transmitter circuit, the PA
controller 202 finds the optimum level of supply voltage 208 by
adjusting the supply voltage 208. If the supply voltage 208 to the
PA 104 is initially higher than the optimum level, the supply
voltage 208 to the PA 104 is decreased. As the supply voltage 208
is decreased, the operating point of the PA 104 approaches closer
to a saturation point where there is less voltage headroom for the
PA 104 to operate. This results in increased distortion in the RF
output signal 110 which is shown as an increase in the measured
activity of the amplitude error signal 218. The increase in
amplitude error signal 218 leads to an increase in the deviation
signal 250. When the distortion of the RF output signal 110
increases beyond the allowable level as defined by the
predetermined distortion level control signal 212, the supply
voltage control signal 224 from the error amplifier 352 is
increased, causing the power supply 299 to provide a higher supply
voltage 208 to the PA 104. When the supply voltage 208 is
increased, the operating point of the PA 104 shifts away from the
saturation point to an operating point where the PA 104 has more
voltage headroom, resulting in a decrease of distortion in the RF
output signal 110. This in turn leads to the decrease in the
measured activity of the amplitude error signal 218 and decrease in
the deviation signal 250. When the deviation signal falls 250 below
the predetermined distortion level control signal 212, the supply
voltage control signal 224 is now decreased, causing the power
supply 299 to provide a lower supply voltage 208 to the PA 104. By
increasing or decreasing the supply voltage 208, the supply voltage
208 is adjusted to an optimum voltage level where the distortion in
the RF output signal 110 corresponds to a predetermined allowable
level set by the distortion level control signal 212. The supply
voltage 208 in essence operates as a bias control signal that
controls the operating point of the PA 104.
[0036] The supply voltage 208 is adjusted optimally even when
changes occur in the impedance of the circuitry receiving the RF
output signal 110. The PA 104 may normally drive circuitry usually
consisting of a filter and an antenna, with a typical impedance of
50 Ohms. However, if the antenna is touched or the cellular device
is laid down on a metal surface, the load presented by the
circuitry receiving the RF output signal 110 is changed, which
changes the operating point of the PA 104. The optimum voltage
level of the supply voltage 208 thus changes. The PA controller 202
then increases or decreases the supply voltage 208 to match the
allowable distortion level set by the distortion control signal
212, to a new optimum voltage level as described above. Therefore,
the PA controller 202 can maintain a high efficiency while
maintaining the level of distortion in the RF output signal 110
even when the load presented to the PA 104 changes.
[0037] Both the output power as well as the PAR of the RF output
signal 110 may change frequently in modern cellular systems. For
example, UMTS mobiles may change transmit power levels at least
once per 667 usec in a closed loop power control scheme controlled
by the basestation, and additionally may handle transmit power
bursts due to special control signaling at other times. UMTS
mobiles also must accommodate transmit modulation PAR changes when
the modulation scheme is changed to accommodate higher datarates.
An increase in either the output power or PAR of the RF output
signal 110 may cause the operating point of the PA 104 to move
closer towards compression, resulting in a higher level of
distortion. The PA controller 202 responds by increasing the supply
voltage 208 until the distortion matches the allowable distortion
level set by the distortion control signal 212, resulting in a new
optimum voltage level as described above. A decrease in either the
output power or PAR of the RF output signal similarly causes the PA
controller 202 to respond by decreasing supply voltage 208. Thus,
the PA controller 202 can maintain a high efficiency while
maintaining the level of distortion in the RF output signal 110
even when the RF output power or PAR of the RF output signal 110
changes dynamically.
[0038] The components of the PA controller 202 may be enabled in
intervals and disabled between the intervals to decrease the power
consumption of the PA controller 202. That is, once the PA
controller 202 has set the supply voltage 208, some of the
components of the PA controller 202 may be disabled during periods
when the operating conditions (e.g. output power, frequency, PAR,
impedance mismatch) of the PA 104 remain approximately static while
holding constant the supply voltage 208, thus decreasing the
overall power consumption of the PA controller 202.
[0039] Further, the power consumption of the power supply 299 may
be reduced during the periods when the PA controller 202 is
disabled. Since the PA supply voltage 208 is held constant during
this period, the PA power supply 299 may reduce its operating
supply current and thus operate in a more efficient,
reduced-bandwidth "slow" mode. During the intervals when the PA
controller 202 is enabled, the power supply 299 may revert to
operation in a "fast" mode in which it is capable of rapidly
changing its output voltage 208 in response to the PA controller
202. In this mode, the power supply 299 may operate with higher
supply current because it must support higher bandwidth required to
rapidly slew the output voltage 208.
[0040] Adjusting the supply voltage 208 may cause some change in
the gain of the PA 104. If the gain change causes an unwanted error
in the power level at the RF output signal 110, the RF input signal
204 may be adjusted in amplitude to compensate the unwanted error,
thus ensuring that the RF output signal 110 maintains an accurate
power level. For example, the TXIC 102 may adjust the amplitude of
its RF signal 204 based on a measurement of the power at the RF
output signal 110 (measurement not shown). Alternatively, the PA
104 may be characterized so that the change in its gain is known
for a change in the supply voltage 208, and thus the TXIC 102 may
adjust the amplitude of its RF signal 204 based on this information
and the supply voltage 208.
[0041] FIG. 3A illustrates an RF PA system, according to a first
embodiment of the present invention. The RF PA system includes,
among other components, the PA 104, the PA controller 202A, an
adjusted variable attenuator (RFFA (RF Feedback Attenuator)) 306,
and a power supply 299'. The PA controller 381 includes, among
other components, a comparator 308, a DC blocking module 340, a
deviation detector 348, an error amplifier 352, a track and hold
(T/H) module 356, and two matched amplitude detectors 302, 304. The
power supply 299' may include a splitter 312, a linear regulator
338, a switched-mode power supply (SMPS) 341, and a power combiner
386.
[0042] Referring to FIG. 3A, the amplitude of the RF input signal
204 is monitored through the amplitude detector 302 and compared by
the comparator 308 with the amplitude of the RF input signal 110 as
attenuated 326 by the adjusted variable attenuator (RFFA) 306, seen
through a matched amplitude detector 304. Note that the amplitude
detectors 302, 304 and the comparator 308 of FIG. 3A correspond to
the amplitude comparator 228 of FIG. 2. The attenuator 306 may be
adjusted such that the output 110 of the PA 104 is attenuated to
have an amplitude level corresponding to the amplitude level of the
RF input signal 204. This can be achieved through programming 321
the variable attenuator (RFFA) 306 by either a digital input to the
PA controller 202 or by analog control of the variable attenuator
(RFFA) 306.
[0043] In this example, amplitude detectors 302 and 304 are log
detectors. That is, the amplitude detectors 302, 304 detect the
logarithm 323 of the amplitudes of the RF input signal 204 and the
logarithm 322 of the attenuated 326 RF output signal 110, to
generate the logarithm of the respective amplitudes 322, 323 at
input and output of the PA 104. It should be understood that an
approximation to logarithm may result from a practical implantation
in the system.
[0044] Therefore, in this example, the comparator 308 generates an
amplitude error signal 309 indicating the difference between the
logarithm 323 of the amplitude of the RF input signal 204 to the PA
104 and the logarithm 322 of the amplitude of the attenuated
version 326 of the RF output signal 110. Thus, the activity of
amplitude error signal 309 is a measure of the distortion generated
by the PA. Note that a benefit of the comparator 308 generating the
difference between the logarithms of the amplitudes, rather than
the difference between amplitudes, can be seen from the equations
below:
Case 1: Comparator 308 Generates Difference Between Amplitudes:
[0045] cout(t)=s(t)-A*(s(t)+e(t))
Case 2: Comparator 308 Generates Difference Between Logarithms of
Amplitudes:
[0046] cout ( t ) = log ( A * ( s ( t ) + e ( t ) ) - log s ( t ) =
log A + log ( s ( t ) + e ( t ) ) - log s ( t ) = log A + log ( s (
t ) + e ( t ) / s ( t ) ) ##EQU00001##
where cout(t) is the amplitude error signal 309, s(t) is the RF
input signal 204, A is the static ratio between the amplitudes of
the RF input signal 204 and attenuated RF output signal 326 as
detected by detectors 302, 304, and e(t) is the error added by the
PA 104 to the RF input signal 204. If the RFFA 306 is adjusted
accurately such that the RF output signal 110 of the PA 104 is
attenuated to have an amplitude level corresponding to the
amplitude level of the RF input signal 204, the value of A
approaches 1. In Case 1, any deviation from A=1 affects the
amplitude error signal 309 cout(t), thus requiring the RFFA 306 to
be accurately adjusted to discern an accurate estimation of
distortion by the deviation detector 348. In Case 2, the term log
A, which is a DC (Direct Current) term, can be removed by a
highpass filter. Thus, the AC (Alternating Current) components at
the amplitude error signal 309 can be used by deviation detector
348 to produce an accurate representation of the distortion, even
if the RFFA 306 is not accurately adjusted.
[0047] The DC blocking module 340 and the deviation detector 348 of
FIG. 3A function as the deviation measuring module 216 as
illustrated in FIG. 2. Specifically, the amplitude error signal 309
is fed into the DC blocking module 340. The DC blocking module 340
blocks DC components of the amplitude error signal 309 and passes
AC components 342 of the amplitude error signal 309. The AC
components 342 are indicative of the activity in the amplitude
error signal 309. Note that the AC components 342 that pass the DC
blocking module 340 may not be all of the AC components of the
amplitude error signal 309 because the DC blocking module 340 may
block or attenuate part of the AC components of the amplitude error
signal 309 in addition to the DC component of the amplitude error
signal 309. The AC components 342 from the DC blocking module 340
are provided to the deviation detector 348.
[0048] The deviation detector 348 generates a deviation signal 350
from the AC components 342 of the amplitude error signal 309. The
deviation signal 350 represents the activity in the amplitude error
signal 309. In one example, the deviation signal 350 is an averaged
magnitude of the AC components 342 of the amplitude error signal
309 over a certain amount of time. In this case, a circuit which
rectifies the AC components 342 of the amplitude error signal 309,
followed by a lowpass filter may be used as the deviation detector
348, for example. The cutoff frequency of the lowpass filter must
be chosen to settle quickly while providing sufficient averaging to
ensure a consistent result. In another example, the deviation
signal 350 is a peak excursion of the AC components 342 of the
amplitude error signal 309 over a certain amount of time. The peak
excursion refers to the magnitude of the highest crest or the
lowest trough of the AC components 342 within a certain amount of
time. In yet another example, the deviation signal 350 is generated
from the AC components using a combination of both the averaged
value and the peak excursion. Note that other methods may be used
to obtain the deviation signal 350 from the AC components 342.
[0049] The accuracy of the deviation detector 348 in representing
the level of distortion at the RF output signal 110 is degraded
somewhat by the delay between the RF input signal 204 and the RF
output signal 110, caused primarily by the delay through the PA
104. During periods when the signal amplitude at the RF input 204
is changing very rapidly, this delay may result in a temporary
peaking of the difference in amplitude between RF input signal 204
and RF output signal 110, which is detected by the comparator 308.
This results in a corresponding peaking of the amplitude error
signal 309. Since deviation signal 350 is based on the AC
components 342 of the amplitude error signal 309, the deviation
signal 350 may indicate a higher level of distortion than
exists.
[0050] In this case, two methods may be used to improve the
accuracy of the deviation signal 350. First, a delay (not shown)
may be added to delay the detected amplitude of the input RF signal
204, such that this delay is approximately equal to the delay of
the PA 104. The delay may be placed before or after amplitude
detector 302. Thus, the RF input signal 204 to the PA 104 and the
RF output signal 110 from the PA 104 are more accurately aligned in
time, reducing the temporary peaking of the difference in amplitude
between the RF input signal 204 and the RF output signal 110. This
improves the accuracy of deviation signal 350. Second, large peaks
in the difference in amplitude between RF input signal 204 and RF
output signal 110, which generate peaking of amplitude error signal
309, may be ignored by the deviation detector 348. For example, a
peak limiter may be used to limit the maximum level of amplitude
error signal 309 to which the deviation detector 348 responds.
Alternatively, since rapid amplitude changes may be associated with
deep nulls in the amplitude modulation at RF input 204, deviation
detector 348 may ignore or reduce its response to the AC components
342 of the amplitude error signal 309 during these periods. In
either case, the accuracy of the deviation signal 350 is
improved.
[0051] The error amplifier 352 compares the deviation signal 350
with the distortion level control signal 212 and generates a supply
voltage control signal 358. The supply voltage control signal 358
may be filtered by a low pass filter (not shown) to provide
stability to the control of the supply voltage 360. The supply
voltage control signal 358 is then provided to the T/H module
356.
[0052] The T/H module 356 operates in a track mode when an
amplitude detect enable signal 366 is active, and in a hold mode
when the amplitude detect enable signal 366 is inactive. In the
track mode, the T/H module 356 generates a track and hold signal
(T/H signal) 360 that tracks the supply voltage control signal 358.
In the hold mode, the T/H module 356 maintains the T/H signal 360
at a constant level. This constant level may be the same as the
supply voltage control signal 358 at the most recent time the T/H
module 356 transitions from the track mode to the hold mode.
[0053] The configuration for the T/H module 356 shown in FIG. 3A is
just an example. Any configuration which allows power supply 299'
to be controlled in two possible modes: (a) by the supply voltage
control signal 358, or (b) by a fixed value such as the supply
voltage control signal 358 at the most recent time the T/H module
356 transitions from the track mode to the hold mode, is allowed.
For example, the T/H module 356 may alternatively be connected
between the deviation detector 348 and the error amplifier 352.
[0054] The power supply 299' generates the supply voltage 208 based
upon the track and hold signal 360 that tracks or holds the supply
voltage control signal 358, and provides the supply voltage 208 to
one or more supply voltage pins of the PA 104. Thus, the supply
voltage 208 may be changed when the T/H module 356 operates in the
track mode, and remains static when the T/H module 356 operates in
the hold mode. Use of the T/H module 356 allows a reduction in the
average power consumption of the PA controller 202, as described
previously.
[0055] Typically, the power supply 299' will comprise a SMPS, to
ensure an efficient delivery of power to PA 104. In some cases, it
may be advantageous that the power supply 299' be capable of
changing its voltage rapidly, while still maintaining an efficient
power delivery. For example, in a UMTS system, when changes to
either transmitted output power or PAR of the RF output signal 110
are required by the basestation, the mobile must make this change
and settle to the specified new transmit power level and PAR in
less than 50 usec, often while maintaining the specified peak code
domain error (peak code domain error is a measure of transmitted
signal distortion). Since a change to transmitted output power or
PAR of the RF output signal 110 may cause power supply controller
202A to adjust the power supply 299' to a new supply voltage 208,
the power supply 299' must be capable of adjusting this voltage
within 50 usec, and may require that the voltage to be controlled
during the change of transmitted output power or PAR of the RF
output signal 110, to maintain an acceptable level of distortion in
the RF output signal 110. In one example of the embodiment of FIG.
3A, the power supply 299' comprises two separate power controllers,
the linear regulator 338 and the SMPS 341. The T/H signal 360
(corresponding to the supply voltage control signal 358 in the
track mode) is split into two signals: a high frequency signal 330
that is fed into a high frequency path including the linear
regulator 338, and a low frequency signal 332 that is fed into a
low frequency path including the SMPS 341. The high frequency
signal 330 is input to the linear regulator 338, which generates
the high frequency part 382 of the supply voltage 208 from the
supply voltage V.sub.CC.sub.--.sub.LIN 210. The low frequency
signal 332 is input to the SMPS 341, which generates the low
frequency part 384 of the supply voltage 208 from the supply
voltage V.sub.BATT 210. The linear regulator output 382 of the
linear regulator 338 and the SMPS output 384 of the SMPS 341 are
combined in the power combiner 386 to generate the supply voltage
208 to the PA 104. For example, a simple current adding node, a
small, high frequency transformer or other types of active
electronic solutions can be used as the power combiner 386. Any
other types of power combiner circuits may be used as the power
combiner 386. The power combiner 386 combines the high frequency
part 382 and the low frequency part 384 to generate the supply
voltage 208 to the PA 104.
[0056] The high frequency signal 330 is comprised of components of
the T/H signal 360 higher than a predetermined frequency, and the
low frequency signal 332 is comprised of components of the T/H
signal 360 lower than the predetermined frequency. The
predetermined frequency used to split the comparison signal 309 can
be set at any frequency, but is preferably set at an optimum point
where the efficiency of power supply 299' is acceptable and the
supply voltage 208 responds to the supply voltage control signal
358 with sufficient speed. In some examples, the predetermined
frequency may not be fixed but may be adjusted dynamically to
achieve optimum performance of the RF transmitter system.
[0057] Note that the two path power supply 299' of FIG. 3A may be
replaced by a simplified or more complex power supply. A simplified
power supply with either a linear regulator or a SMPS may be used,
although the efficiency of the RF transmitter system may be
somewhat decreased. A more complex power supply further increasing
the efficiency of the RF transmitter may also be used. For example,
it is possible to split the amplitude correction signal 309 into
more than two different frequency ranges for separate processing by
adjustable power supply components.
[0058] In another example of the first embodiment, one or more
components of the PA controller 202 are implemented by a digital
signal processor (DSP). For example, the T/H module 356 is
implemented by the DSP. Using the DSP as the T/H module 356 has the
advantage that a hold signal from the DSP does not diminish with
the progress of time unlike a hold signal from a T/H module
implemented by a capacitor. Alternatively, the comparator 308, the
DC blocking module 340, the deviation detector 348, the error
amplifier 352, and the T/H module 356 may be replaced with the DSP.
In this case, the DSP receives the amplitude 323 of the RF input
signal 204 and the amplitude 322 of the RF output signal 110, and
generates the supply voltage control signal 360. The DSP can also
be advantageously used to implement additional signal processing
and control schemes to increase the efficiency of the RF
transmission system.
[0059] FIG. 3B illustrates an RF PA system, according to a second
embodiment of the present invention. In the embodiment of FIG. 3B,
the PA controller 202B further includes a variable gain amplifier
(VGA) 336. The VGA 336 is introduced in the RF signal path between
an RF input 204 and a PA input 206. A VGA control module 380 is
coupled to the comparator 308 to receive the amplitude error signal
309 to generate a gain control signal 392 based on the amplitude
error signal 309. The VGA control module 380 may filter the
amplitude error signal 309 to more stably control the VGA 336.
[0060] The VGA 336 receives the RF input signal 204 and generates
the RF PA input signal 206. The VGA control module 380 generates a
gain control signal 392, which controls the gain of the VGA 336
based upon the amplitude error signal 309 in a control loop that
attempts to minimize the difference between the RF output signal
110 and an attenuated RF input signal 204. Thus, the gain of the RF
output signal 110 relative to the RF input signal 204 is maintained
constant, and the VGA 336 helps to form a closed loop that
effectively performs linearization of the PA 104. The linearization
of the PA 104 decreases the distortion of the RF output signal 110
from the PA 104. Therefore, when the VGA 336 is used, the supply
voltage 208 to the PA 104 can be decreased more than when the VGA
336 is not used. This results overall increase in the efficiency of
the RF transmitter system.
[0061] Like the first embodiment in FIG. 3A, various components of
the PA controller 202B in FIG. 3B can be replaced with a DSP.
[0062] FIG. 3C illustrates an RF PA system, according to a third
embodiment of the present invention. The RF PA system illustrated
in FIG. 3C is substantially the same as the RF transmitter circuit
illustrated in FIG. 3B, except that (i) the amplitude error signal
309 is fed only to the VGA control module 380 and not to the DC
blocking module 340, (ii) the gain control signal 392 is fed to the
DC blocking module 340 in place of the amplitude error signal 309,
and (iii) the PA controller 202C further includes a T/H module
376.
[0063] In the embodiment of FIG. 3C, the output signal 342 from the
DC blocking module 340 is the AC components of the gain control
signal 392. The gain control signal 392 is an amplified version of
the amplitude error signal 309; and therefore, the function and
operation of the DC blocking module 340, the deviation detector
348, the error amplifier 352, and the T/H module 356 are the same
as the embodiment of FIG. 3B except that the gain control signal
392 is used in place of the amplitude error signal 309. Because the
gain control signal 392 is an amplified version of the amplitude
error signal 309, the gain control signal 392 has larger amplitude
compared with the amplitude error signal 309. The embodiment of
FIG. 3C is advantageous because the gain control signal 392 has a
larger signal level which is easier to process compared to the
amplitude error signal 309.
[0064] Additionally, the gain control signal 392 (via a T/H signal
385) may control VGA 336 in a linear-in-dB manner. That is, a
linear change in signal level at the gain control signal 392 may
result in a logarithmic (dB) change in the gain of the VGA 336.
Thus, the gain control signal 392 is indicative of the difference
between the logarithm of the amplitude 323 of the RF input signal
204 and the logarithm of the amplitude 322 of the attenuated RF
output signal 326, and so offers similar advantages to those
described for the amplitude error signal 309 indicating the
difference between the logarithm of the amplitude 323 of the RF
input signal 204 to the PA and the logarithm of the amplitude 322
of the RF output signal 110 as described above with reference to
FIG. 3A. In this case, the AC components at comparator output 309
can be used by the deviation detector 348 to produce an accurate
representation of the distortion, even if the RFFA 306 is not
accurately adjusted.
[0065] In this example, the gain control signal 392 from the VGA
control module 380 is provided to a T/H module 376. The T/H module
376 includes a switch 373, a lowpass filter 371, and a T/H
component 372. The T/H module 376, like the T/H module 356 operates
in a track mode when the amplitude detect enable signal 366 is
active, and in a hold mode when the amplitude detect enable signal
366 is inactive. In the track mode, the switch 372 is coupled to a
first path 377 so that the T/H module 376 outputs a T/H signal 385
that tracks the gain control signal 392. In the hold mode, the
switch 372 is coupled to a second path 379 that includes the
lowpass filter 371 and the T/H component 372. Note that the lowpass
filter 371 may perform an averaging function, and the averaging
period may be adjustable or fixed. Therefore, in the hold mode, the
T/H component 372 maintains the T/H signal 385 same as the average
value of the gain control signal 392, at the most recent time it
transitions from the track mode to the hold mode. The T/H signal
385 is input to the VGA 336 to control the gain of the VGA 336.
[0066] The T/H module 376 provides two advantages. First, it may
allow VGA 376 to operate at a lower average current. During the
period when the amplitude detect enable signal 366 is active and
the T/H module 376 is in track mode, the VGA control 380 and the
VGA 336 together with other components of the RF power amplifier
system form a closed loop that performs linearization of the PA
104, as described previously. During this time, the AC component of
gain control signal 392 is used by the deviation detector 348 to
determine an approximation of distortion at the RF output 110, and
the supply voltage 208 may be adjusted during this interval. When
the amplitude detect enable signal 366 is inactive and the T/H 376
is in hold mode, the VGA 336 may be held at a constant gain level,
and thus the VGA 336 may be biased at a lower current suitable for
this static level.
[0067] Second, during the T/H track mode, the averaged gain control
signal 392, as monitored by the T/H module 376, corresponds to the
average gain of VGA 336 required to maintain a constant gain of the
RF output signal 110 relative to the RF input signal 204,
compensating for gain changes in the PA 104 when the supply voltage
208 is adjusted. At the time when the T/H module 376 enters the
hold mode, the gain of VGA 336 is fixed to the level corresponding
to the recently averaged gain control signal 392, which corresponds
to the gain required to compensate for the gain of PA 104 at that
time. If the operating conditions for the PA 104 remain relatively
static (e.g. with respect to output power, frequency, PAR,
impedance mismatch), and the supply voltage 208 does not change
because the T/H modules 356, 376 are both placed together into hold
mode by the amplitude detect enable signal 366, this fixed gain of
the VGA 336 is set properly for the period in the hold mode.
[0068] The details shown in FIG. 3C for the T/H module 376 are just
an example. Any configuration which allows the gain of the VGA 336
to be controlled in two possible modes: (a) by the gain control
signal 392, or (b) by a fixed value such as the averaged gain
control signal, responsive to the amplitude detect enable signal
366, is allowed. For example, the lowpass filter 371 may be swapped
with the T/H component 372.
[0069] Like the first embodiment in FIG. 3A, various components of
the PA controller 202C of FIG. 3C can be replaced with a DSP.
[0070] The RF power amplifier systems depicted in FIGS. 3B and 3C
may be combined in any way. For example, while FIG. 3B shows an RF
power amplifier system without the T/H module 376 as shown in FIG.
3C, the T/H module 376 may be included in the system shown in FIG.
3B. In this case, the VGA 336 may be operated in a track or hold
mode as described above with reference to the embodiment of FIG.
3B. While the VGA 336 no longer provides closed loop linearization
as described previously during the hold mode, the VGA 336 does
correct for gain changes in the PA 104 while the supply voltage 208
is adjusted.
[0071] In another example, FIG. 3C shows the gain control signal
392 feeding the DC blocking module 340. Alternatively, the
amplitude error signal 309 may instead feed the DC blocking module
340. Thus, the deviation detector 348 may base its deviation signal
350 on the amplitude error signal 309.
[0072] FIGS. 4A and 4B illustrate a method of controlling the RF PA
system, according to the first and second embodiments of the
present invention. Note that the processes common to the first and
second embodiments are shown in blocks with solid lines whereas the
processes performed by the second embodiment but not the first
embodiment are shown in blocks with dashed lines.
[0073] In the first and second embodiments, the amplitude detect
enable signal 366 is sensed to determine 402 whether the amplitude
detect is active. In the first and second embodiments, if the
amplitude detect is active, the amplitude of the RF input signal
204 and the attenuated amplitude of RF output signal 110 are
compared to generate 404 the amplitude error signal 309. In the
second embodiment, the amplitude error signal 309 is amplified (and
filtered, if needed) to generate 406 the gain control signal 392.
In the first embodiment, the step 406 is not carried out.
[0074] In the first and second embodiments, the DC blocking module
340 blocks 410 the DC component of the amplitude error signal 309
and passes 410 the AC components 342 of the amplitude error signal
309. Then, the deviation signal 350 is generated 412 from the AC
components 342 of the amplitude error signal 309. The deviation
signal 350 is then compared 414 with the distortion level control
signal 212 to generate 414 the supply voltage control signal 358.
The T/H module 356 generates the T/H signal 360 that tracks 416 the
supply voltage control signal 358.
[0075] The supply voltage control signal 358 (in the form of the
T/H signal 360) is provided to the power supply 299' to generate
424 the supply voltage 208. The supply voltage 208 is then provided
426 to the PA 104. In the second embodiment, the gain of the VGA is
adjusted 428 based on the gain control signal 392. In the first
embodiment, the step 428 is not carried out.
[0076] In the first embodiment, the process returns to the step 402
after finishing the step 424. In the second embodiment, the process
returns to step 402 after finishing the step 428. Note that the
steps 406 and 428 can be performed in parallel with steps 410
through 426.
[0077] If it is determined in step 402 that amplitude detect is
inactive, the process proceeds to hold 440 the supply voltage
control signal 358 at the most recent value at the track mode
before the transition. Then the process proceeds to the step 418 of
splitting the T/H signal 360.
[0078] FIGS. 5A and 5B illustrate a method of controlling the RF PA
system, according to the third embodiment of the present invention.
The method illustrated in FIGS. 5A and 5B is substantially the same
as the method illustrated in FIGS. 4A and 4B, except that (i) the
AC Components 343 of the gain control signal 392 (instead of the
amplitude error signal 309 as in the first and second embodiments)
is filtered in step 510, that (ii) the deviation signal 350 is
generated from the AC components of the gain control signal 392
(instead of the amplitude error signal 309 as in the first and
second embodiment) in step 512, and that (iii) the gain control
signal is held when the amplitude detection is disabled in step
542. All the other steps in the method according to the second
embodiment in FIGS. 5A and 5B are substantially the same as the
method according to the first and second embodiments in FIGS. 4A
and 4B. Note that the steps in FIGS. 5A and 5B different from the
steps of FIGS. 4A and 4B are shown in blocks with bold solid
lines.
[0079] Upon reading this disclosure, those of skill in the art will
appreciate still additional alternative structural and functional
designs for the RF power amplifier controller through the disclosed
principles of the present invention. For example, the T/H module
can be coupled to the deviation detector to track and hold the
deviation signal instead of the supply voltage control signal. The
power amplifier controller circuit can be used with any type of
power amplifier for many different types of electronic devices,
although the embodiments are described herein with respect to a RF
PA controller used in cellular telephone applications. Examples of
these applications include video signals and Manchester coded data
transmissions. For another example, digital techniques can be used
to process some of the signals of the PA system described herein.
Whether a signal is represented in an analog form or a digital form
will not change the functionality or principles of operation of the
PA system according to various embodiments of the present
invention.
[0080] Thus, while particular embodiments and applications of the
present invention have been illustrated and described, it is to be
understood that the invention is not limited to the precise
construction and components disclosed herein and that various
modifications, changes and variations which will be apparent to
those skilled in the art may be made in the arrangement, operation
and details of the method and apparatus of the present invention
disclosed herein without departing from the spirit and scope of the
invention as defined in the appended claims.
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